Process for producing concentrated hydrofluoric acid



July 14, 193., .1, c. LAWRENCE PROCESS FOR PRoDucNG CONCENTRATED HYDROFLUORIG ACID Filed July 18, 1954 2 sheets-sheet 1 www@ IN V EN TOR.

July 1 4, 1936. v J. c. LAWRENCE v 2,047,210

PROCESS FOR PRODUCING CONCENTRATED HYDROFLUORIC ACID Filed July 18, 1934 2 Sheets-Sheet 2 A TTORNEY.

Patented July 14, 1936 PROCESS FOR PRODUCING COlilCEl'llifATED4 HYDROFLUORIC ACID James C. Lawrence, Meylan, Pa., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application July 1s, 1934, sei-iai No. 135,813 l l1o claims.' (cica-15s) l This invention relates to hydrouoric acid, more particularly concentrated hydroiluoric acid,

.and a process for the production thereof.

`It is known that hydrouoric acid may be produced by the reaction of sulfuric acid with a mineral fluoride. According to previous processes, however, considerable difficulty has been experienced in the production of concentrated hydroiiuoric acid because of the trouble encounteredin removing water vapor from the product. While it has previously been proposed to remove water from the hydroiiuoric acid vapors by passing them through dehydrating materials such as concentrated sulfuric acidJ oleum or sulfates of the alkaline earth metals, such processes are usually impractical or inoperable on 'account of side spar, which is then mixed with sulfuric acid, and' heat applied. The hydrofluoric acid 'gas which ls .evolved is.,recovered in Aa suitable absorber or condenser, and at the conclusion of the operation it is necessary todisassemble the reaction vessel and remove the hard, solid residue preparatory to the introduction of a, fresh charge. Obviously, a, process and apparatus of this character necessarily have a limited output or capacity and leave much to be desired from an economic standpoint. Furthermore, this method of producing hydroiluoric acid yields directly only a relatively dilute acid rather than a highly concentrated acid.

It is an object of the present invention to provide a new and improved process for the produc- ,tion of concentrated hydroiluoric acid. Another object is the provision of a continuous process for the production of hydroiluoric acid by a procedure which enables the recovery of both relatively dilute hydroiluoric acid and highly concentrated hydroiluoric acid from the same operation. A

still further object is the provision' of a method for producing hydroiluoric acid from an acid and a fluoride by an improvement which enables the amount of water present in the evolvedreaction the accompanying drawings, in which similar l what diagrammatic, of one form of apparatus for carrying out the process of the invention;

A form of the portion of the apparatus shown in vapors to be substantially reduced. An additional object is the provision of a process involving a series of steps which lead to the production of concentrated hydroiluoric acid in high yields and in a high state of purity. Other objects will appear hereinafter. v

tion of concentrated and relatively dilutehydro-lo fiuoric acid and characterized by: (l) the formation of hydroiuoric acid by the reaction ofma uoride and an acid under super-atmospheric pressure; (2) continuously introducing the re1- actants into the reaction zone and continuousl withdrawing the reaction products while main- -taining super-atmospheric pressure; (3)' sub'- jecting the evolved vapors containing hydro-- iluoric acid 'to a preliminary condensation at suitable' temperatures to effect the separation of relatively dilute hydrofluoric acid; and (4) condensing the residual gas or vapor. The final condensate is a concentrated hydrouoric acid suitable for use in a wide variety of chemical operations. 'I'he condensate obtained in step 3 is a less concentrated hydrofluoric acid which may be used 'as such -or further` concentrated in any suitable manner, preferably by vaporization v in a fractionating column and subsequentecon'- densation of the vapors.

The apparatus falling within the invention is subject to considerable variation and modification in the manner of its practical construction but may be illustrated by the forms of apparatus in numbersrefer to similar parts throughout the several views and description thereof.V v In the drawings:

Fig. 1 is a side view, partly in section and some- Flg. 2 is a profile or end view, partly in section, of a portion of the apparatus shown in Fig. 1;

Fig. 3 is a view partly in'section of a modied Fig. 2.

Referring to Fig. l of the drawings, the apparatus illustrated comprises generally a reactor-A and a means of introducing thereactants, namely an acidand a iluoride, into the reactor A from a suitable storage container for the reacting acid, generally illustrated at B, and a container for the fluoride, generally illustrated at C. The gases containing` hydrofluoric acid evolved by the reaction are passed through a purifying means, 5s

such as illustrated at D, in order to remove dust and acids other than hydrofluoric acid which may be present. rI'he resultant vapors are then subjected -to a preliminary cooling or fractional condensation in a suitable manner, for example, by means of a fractional condenser such as generally illustrated at E, the condensate being collected by a convenient method as illustrated, for instance, by the storage container indicated at F. A vessel G is provided for the removal of mist. The gases or vapors remainingiafter this preliminary condensation are then introduced into a final condenser, such as illustrated at H. 'I'he condensate from H, together with any uncondensed gases, is passed through a suitable means for separating the uncondensed gases, such as shown at K, and the resultantl concentrated hydrouoric acid is collected in a suitable storage vessel generally indicated at L. The concentration of this acid may vary somewhat depending largely upon the raw materials and the operating conditions but under the preferred conditions oi' operation is usually 95 to 99%.

The less concentrated hydrofluoric acid contained in the storage vessel F may be used as such for various purposes, or it may be introduced into the distillation column N by way of storage vessel M and subjected to a'fractional distillation treatment whereby anhydrous hydroiluoric acid is obtained by the condensation of the vapors in the condenser O, and a constant boiling mixture of the acid remains as a residue in still-pot 8i..

The detailed operation of the process of the invention may be conveniently illustrated with reference to specific reactants, sulfuric acid and fluorspar. Finely ground fluorspar is introduced into the storage equipment indicated at C, which comprises a container I provided with a valved inlet 2 for the iinely ground iiuorspar and a valved. vent 3. From container I the fluorspar passes through a bottlom outlet 4 into' an enclosed screw conveyor 5 operated by a suitable means, such as, for example, a motor 8; From the screw conveyor 5 the iluorspar is introduced by way of lines 1' and 8 into suitable receivers or hoppers 9 and I0, respectively, which connect through an enclosed funnel I2 with a vertical screw conveyor I l which maybe operated by a motor of suitable design (not shown). The screw conveyor II discharges the fluorspar against a positive or superatmospheric pressure into one end of the retort indicated at A. sulfuric acid is introducedinto the retort A through a line I5 and valve I6 leading from a sulfuric acid storage, generally indicated at B and comprising a container I3 provided with a valved sulfuric acid inlet I4.

As an alternative method of operation, the vertical screw conveyor II may discharge fluorspar against a positive or super-atmospheric pressure into a pre-mixing mill along with the sulfuric acid through line I5 and valve I5 from a sulfuric acid storage. This pre-mixing'mill will then deliver the mixed uorspar and sulfuric acid in the form of a paste into the end of the retort A. In this manner, the retort may be shortened as the mixing is done externally and not in the iirst section of the heated retort.

The reactor indicated at A, as shown, comprises y a U-shaped retort I1 which is closed for operating under positive or super-atmospheric pressure by means of a cover I8. Within the retort I1 is a device for agitating the reaction mixture consisting of radial arms 20 operating on a central drive shaft I9 which, in turn, is operated by a suitable means such as, for example, a motor illustrated at 2i. The retort is inclined in order to facilitate the continuous passage of the reaction mixture away from the zone of introduction oi the reactants. A heating means, such as indicated by the furnace at 2B. is provided vto maintain the desired temperature in the retort. In operating the process, it has lgenerally been found desirable to increase the temperature oi the reaction mixture as it is forced away from the zone oi introduction of the reactants. The non-gaseous reaction products which, in case a mineral fluorspar is used initially, comprise substantially calcium sulfate are removed from the reaction zone by a special continuous discharge device shown at 22, which is capable of effecting thev discharge while maintaining super-atmospheric pressure in the reaction zone. This device is operated by shaft 24 which is synchronized with the central drive shaft I9- in any suitable manner, for example, by means of an arrangement of pulleys and a belt, such as indicated at 23. The pressure in the retort is indicated by pressure gauges 26 and 21.

The gaseous reaction products which may be removed from the retort at any convenient place are preferably withdrawn near the zone of introduction of the reactants through line 23 which connects with the purifier indicated at D. The purier D consists of a container 30 which is filled with a suitable purifying medium such as, for example, coke, indicated at 3I which serves to remove the dust and most of the sulfuric acid mist present in the gas. After passage through the' coke, the remaining gases, comprising substantially hydroiluoric, acid and water, pass through aline 33 into the fractional condenser E. The fractional condenser:E consists of a coil 34 of relatively large diameter which is cooled by water from a water cooler 35. Water cooler 35 is provided with suitable cooling coils containing a refrigerating medium such as, for example, refrigerated brine, which is introduced through a valved inlet 39 and withdrawn through a valved outlet 40. 'I'he water to be cooled is introduced into the water cooler 35 through a valved inlet 36 and the cooling water is withdrawn from cooler 35 through line 31 which connects with the spray device 38. The water from the spray 33 is collected in a suitable open vessel, such as illustrated at 4I, having an outlet 42. Under some climatic conditions water cooler 35 may be omitted from the construction of the apparatus.

lin operating the process. it is desirable that the temperature of the cooling medium for cooling fractional condenser E be such as to maintain the temperature of the coils 34 above but preferably not more than about 15 higher than the boiling point of hydrouorlc acid.

The condensate collected in coils 34 is withdrawn through a line Ill and introduced through valve 63 into storage tank B8. A valved sample line 50 on line 41 is provided to remove test samplesv of the acid obtained. In using the speciiic reactants described, this acid ls normally a relatively dilute hydrouoric acid varying in concentration from about 60% to about 80%: It will be recognized, however, that the concentration of the acid may vary widely depending largely upon the character of the starting materials and the temperature used in fractional condenser E. As previously indicated, this acid may be used ,as such or it may be passed through line 5I and valve 52 to a pump 53 by means of which it may 'upper part of the vessel indicated at G.

be forced through line I6 controlledby valve `61 into a storage tank generally indicated at M. From this storage tank it may then be introducedv through line 11 and valve 1I into the column generally indicated at N and further treated as hereinafter described. Where it is desired to use the relatively dilute hydrofluoric acid as such, it may be Withdrawnl through a valved outlet 58. Aporticn of the relatively dilute hydroiluoric acid collected in storage tank 46 may be circulated through line 5| and valve 52 and forced by a suitable means, such as', for example, pump 53,through line 54 and valve 55 into the vessel consists of a container 44, preferably having on the inside thereof several plates (not shown) such as may be used in a distillation column. Any liquids condensed or introduced into this vessel fall to the bottom, are removed through line or cooling coils 34 and are collected in storage tank 46.

The residual gases pass through line 5s to a condenser generally indicated at H. 'I'his condenser may be of any suitable design adapted to obtain relatively low temperatures. It may be. cooled by direct expansion of a refrigerant such as, for example, carbon vdioxide introduced through a valved inlet line 8| and withdrawn through a valved outlet line 62. 'Ihe condensate is removed through line 63 and any uncondensed gases separated by a suitable means such asindicated at K. The separating means indicated at K consists of a trap 64 having a .valved vent line 65 through which the uncondensed gases may be removed by venting to the atmospherev or in any other suitable manner, for example, by venting t0 a caustic bubbling tank. The concentrated hydroiluoric acid passes through line 66 .and valve I1 into the storage equipment generally indicated at L. The storage equipment L may conveniently comprise a container 6B having a valved bottom outlet 69 through which the concentrated hydrofiuoric acid may be withdrawn for use as such. A line 10 connecting to the upper part of the container $8 and the upper part of the condenser indicated at H is provided to equalize the pressures in these' portions of the apparatus.

For further concentration, the relatively dilute hydroiluoric acid contained in the container 46 may be forced by means of pump 53 through line 58 and valve 51 .to the storage tank, generally indicated at M, from which it may be introduced linto the column through line 11 and valve 1B. If desired, the relatively more concentrated hydrofiuoric acid in storage vessel L may be similarly treated. Column 80, which is maintained at such a temperature that the hydrofiuoric acid is vaporized, serves to remove practically all of the moisture which is present. A less concentrated acid collects in the still pot 8| and may be periodically removed through the valved bottom ,outlet B2. The vapors passing upward through line` 83 are introduced into condenser O. Condenser O may be of a tubular, coiled or of any other suitable to the column N where it serves as a refiuxing 1 liquid. The remainder of the acid may bewithdrawn through line 92 and valve 93. The valved bottom outlet 3| to trap 88 is provided largely for the purpose of draining the trap.

'I'he prole or end view of the retort A, shown partly in section in Fig. 2, illustrates in more detail the type of device which may be used in continuously removing the non-gaseous reaction products while maintaining super-atmospheric pressure. In Fig. 2, the portions of the apparatus shown are the U-shaped retort H1 closed at the top by means of the cover IIB. Within the retort is shown a central drive shaft ||9 and several of the T-shaped agitating devices |20, which are connectedto and driven by the shaft H9. The device for removing the non-gaseous 'reaction products comprises a shell or case |22 which is fastened to the retort at the point |23.

Within this shell |22 and closely iitting to thewalls thereof is an eduction device |25, driven by a shaft` |24 which, in turn, is synchronizedy l with the central drive shaft H9. This'eduction device |25, as shown, is so constructed that at no time in its operation is there a direct passage of air from the outside. Accordingly, by this type of device it is possible to maintain the superatmospheric pressure inside of the retort. The pockets |26 in the eduction device |25 collect the non-gaseous residue as it is continuously forced k through the retort and remove it through the opening |21. The speed of rotation of the eduction device |25 may be regulated according to the amount of non-gaseous residue to be' removed.

In Fig. 3, a modified method of removing-the non-gaseous residue from the retort A is illustrated. The modified retort A is shown in prole, partly in section, comprising the outer casing of the retort 2|1, the top 2|8, the central drive shaft 2 9, and the agitating device, generally indicated at 220. The non-gaseous solid residue is removed from the retort by means of the wormtype conveyor 225 enclosed by a casing 222 and driven by a shaft 224 which connects through a series of gears generally illustrated at 226 with a suitable operating means, such as a motor 221. The residue is discharged through opening 228 into a closed container illustrated at 229. This type ofeduction device is considered to be more elcient than that' illustrated in Fig. 2. since the operationdis such that littleif any,ai,r.may come into the retort through the opening 228, whereas in the device shown in Fig. 2 some air may be encompassed in the pockets |28 and carried into the retort. In either case, however, it is possible to maintain a super-atmospheric pressure as required in accordance with the operation of the process of the present invention.

`In the construction of the various portionsof the apparatus, any non-corrodible or substantially non-corrodible materials may be used. In practice, it has been found desirable to use iron, preferably steel, in constructing the retort A. The storage vessel for the acid B and the collector for the uoride `C may oe made of any suitable materials, such as copper, iron or steel. The purifying tower D may likewise be constructed of copper, iron or steel. The coils 34 in which a relatively dilute hydrouoric acid is present are preferably constructed of copper. The same is true of other portions of the apparatus exposed to the action G is also preferably constructed of copper. The condenser H in which concentrated hydrofiuoric acid is condensed is preferably constructed of copper. The same is true of the separator for uncondensed gases K, but the storage vessel for concentrated hydrouoric acid I is preferably made of steel. The portions of the distillation apparatus illustrated at M, N and O, and the various connecting lines should preferably be constructed of a material which is resistant to both relatively dilute and concentrated hydrofluoric acid such as, for example, copper. Iron materials of construction have given very satisfactory service in the construction of the fractionation apparatus. In general, in the practical construction of the apparatus it is preferable to use iron materials of construction, preferably steel, in all portions of the apparatus exposed to hydrofluoric acid having a concentration greater than about 70%. However, it has been found possible to employ iron materials of construction even where the hydrofluoric acid concentration is as low as 50%, as for example in still-pot 8l. Some corrosion occurs but not enough to prevent commercially satisfactory results. It will be recognized that materials of construction may be varied widely in a manner well known to those skilled in the art.

Various changes may be made in the type of equipment and the arrangement thereof. Thus. various other methods may be used for forcing the reaction mixture through retort A. The purifying tower D may be omitted from the construction of the apparatus, in which ca, however, the hydrouoric acid would contain impurlties such as fluoride, sulfuric acid or the like. Furthermore, various portions of the apparatus would be subjected to clogging on account of the dust carried out oi' the retortI with the gaseous reaction products. Circulation of acid from storage vessel F to vessel G is not essential to operation of the process. The vessel G, together with lines and 54, may be omitted from the construction of the apparatus. One of the purposes of using a plated column G is to remove or scrub out the mist from the gas stream issuing from the fractional condenser E. The cooling medium used in the various portions of the apparatus may vary7 Widely according to the tern- `perature desired.

The invention is further illustrated, but not limited, by the following example, in which the parts are by weight.

Example In an apparatus similar in principle to that described in Figi, fluorspar (containing about 98.5% calcium fluoride and 0.3% silica), ground to a neness of about 300 mesh and carefully dried, was continuously fed into retort A from the fiuorspar storage C against a pressure of about two to rive pounds per square inch (gauge). Sulfuric acid having a concentration of about 98% was also continuously introduced into retort A from the storagervessel B. The proportions of iluorspar to sulfuric acid were so regulated that about 69 parts of fiuorspar to 100 parts of sulfuric acid were used. The reaction proceeded as the reactants were agitated andcarried down the heated vzone of the retort. The temperature of the retort A varied from about 150: (Lat the zone of introduction of the reactants to about 315 C. in the lower end of the retort, the increased temperature toward the end of the retort being maintained by means of a suitably fired furnace. At the discharge end of the retort A the non-gaseous residue comprising substantially calcium sulfate was removed by Ymeans of a special eduction device, such as illustrated in Fig. 2, synchronized with the speed of the retort agitator shaft as described in connection with Fig. 1.

The gaseous reaction products comprising hydrofluoric acid vapors, the water vapor introduced into the retort by the sulfuric acid and fluorspar, and a small amount of sulfuric acid mist passed out of the retort A into the purifier D, which was packed in layers with coke of graduated size. Here, impurities such as dust and about 90% of the sulfuric acid mist were removed by the coke, leaving the hydrofluoric acid vapors and water with about 0.4% sulfuric acid mist or vapor to pass into the fractional condenser E at a temperature of about 150 C.

, The concentration of the vapors entering the fractional condenser E was about 94.5% hydrofluoric acid, 5.1% water and 40.4% sulfuric acid. The fractional condenser E was cooled by a water spray, as shown in Fig, 1, so that the gases were cooled below about 35.6 C. but not lower than about 25.0 C. sulfuric acid, water and hydrofluoric acid condensed out of the vapors at the temperatures given, the condensate flowing out of condenser E into the receiver F as a solution of hydrorluoric acid of approximately 75% strength. The cooled hydroiiuoricacid gas containing only small proportions of water was then passed through column G into condenser H which was maintained at a temperature of about -20 C., and the condensate, concentrated hydrofluoric acid of a purity of about 99%, was collected in the receiver L after venting any uncondensed gases to the atmosphere in the separator K. The average yield of hydrofluoric acid was about 94%.

The less concentrated acid'collected in the receiver F was further concentrated by introducing it into vessel M from which it was fed into the column N maintained at a temperature of about 19.5 C. at the top and about 110 C. at the bottom and in the still-pot 8l. The vapors were condensed by means of condenser O and the condensate, anhydrous hydrofluoric acid, removed through trap 88. A relatively more dilute hydrofluoric acid, having a concentration of about formed in the still-pot 8| and was withdrawn through the valved outlet 82.

The kind and amount of fluoride and acid to be reacted therewith employed in accordance with the yinvention may vary within relatively wide limits, depending largely upon the results desired. In order to produce a highly concentrated hydrofiuoric acid (i. e., above about 90%),

it is preferable to employ a fluoride relatively free from moisture and silica, and a relatively concentrated reacting acid so that the evolved crude gases containing hydrofiuoric acid are also relatively free from moisture, preferably containing less than about 15% Water. For ,this purpose, the uoride employed should preferably contain little or no substances which form volatile impurities, as, for example, silicates, which form silicon tetraflu'oride and fiuosilicic acid, and

carbonates. In practice, it has been found that especially desirable results are obtained in the use of a mineral fluoride such as uorspar, i. e., a uoride comprising substantially calcium fluoride. Fluorspar which has been treated to remove silica may advantageously be employed. As examples of other uorides which may be reacted together with an acid under super-atmospheric pressure to produce hydrouoric acid in accordance with the invention may be mentioned cryolite and the like.

of the free acids, acid sulfates'e. g., sodium acid sulfate, potassium acid sulfate, and the like) may be used. It will be understood, however, that such acids, in general, neither possess the advantages of sulfuric acid nor produce comparable results.

The proportions of fluoride and acid may vary but, ordinarily, it is desirable to use at least the stoichiometrical proportions of acid required to convert theuoride to hydroiiuoric acid, and preferably an excess of acid. In practice, it has been -found that in the reaction of uorspar with concentrated sulfuric acid very good results are obtained in the use of about 5% excess sulfuric acid over the stoichiometrical proportions.

The temperatures maintained in the various steps of the process may vary within relatively wide limits. In the reaction zone the temperature should preferably be at least sufficient to drive off the hydrofluoric acid vapors. As a general rule, it is preferable to maintain the temperature in the reaction zone in excess of about 100 C. It has been found desirable to increase the temperature as the reaction proceeds, this being accomplished in any suitable manner, for

example, by means of a furnace as described in I connection with Fig. 1. lEspecially desirable results have been obtained in effecting the reaction initially at a temperatureI of about C. to about C. and gradually increasing the temperature to above 300 C., preferably about 310 C. to about 320 C.

The temperature of the purifier tower, such as illustrated by D in Fig. 1, should preferably be above the temperature of condensation of. the hydroiluoric acid vapors in the crude gas from the reaction zone. In practice, it is customary to neither heat nor cool the tower D, although it may be heated or cooled if so desired.

As previously indicated, the temperature of the preliminary cooler or fractional condenser, such as illustrated by E in Fig. 1, should preferably be above the boiling point of hydroiluoric acid but not more than about 15 C. higher than theboiling point under the same conditions of pressure. Under conditions of operation where the crude gas comprises substantially hydroiluoric acid and about 5% to 15% water, this enables the recovery very nearly thesame as that of the fractional condenser E, being heated or cooled ordinarily only by the gases and liquids introduced into it.

The temperature of the secondary condenser, such as illustrated at H in Fig. 1, should preferably be below about 20 C. but sumciently high to preserve the condensate in liquid form. While higher condensation temperatures may be used in this step'of the process, the recovery of hydroiluoric acid is more eflicient at the temperatures indicated. .J

-Where it is desired to further concentrate the hydroiiuoric acid such as is recovered in storage vessel F of Fig. 1 by introduction into a fractional distillation apparatus, such as generally illustrated at N, the temperature of the column .N should be sufficient to vaporize the hydrofluoric acid, being preferably about 19.5 C. to 20 C. at the top of the column and about 110 C. at the bottom. The condenser O may bemaintained at any suitable condensation temperature. preferably about -20 C. or lower. In order to effect the vaporization, heat may be applied to the stillpot 8l or to the column N or to both by any suitable means, for example, by means of steam pipes (not shown).

The pressure in the various steps of the process is subject to considerable variation. Ii' desired, all of the steps of the process may be operated under super-atmospheric pressure. cially desirable, however, from the standpoint of the present invention that the reaction involving the formation of the hydrofluoric acid be effected under super-atmospheric pressure` Even a slight superatmospheric pressure improves the results over those obtained by operation at atmospheric or sub-atmospheric pressure. This improvement is manifested in the ability to obtain better eiliciency and more concentrated hydrofiuoricV acid directly than are obtainable by operationunder atmospheric or sub-atmospheric pressure.

The super-atmospheric pressure in the reaction zone may be maintained in any suitable manner, for example, by the introduction of an inert gas, e. g., nitrogen, under super-atmospheric pressure. If such inert gas is introduced, care should be taken that it is substantially free from It is espe- 9 moisture. In practice, it has been found that a` super-atmospheric pressure in the reaction zone of an apparatus such as illustrated in Fig. 1 may vbe maintained by means of the back pressure the method of introducing the reactants and the method of withdrawing the reaction products. Good results may be obtained where the superatmospheric pressure corresponds to about 15 pounds per square inch or even less. 'If desired, much higher pressures may be used. The pressure should preferably be such that, under the temperatre conditions used, substantial condensation of the hydrofluoric acid does not occur in the reaction zone. Above the critical temperature of hydrofluoric acid, any super-atmospheric pressure may be 4used.` A's previously indicated, the pressure in the other portions of the apparatus may be the same as that in the reaction zone, or, if desired, lower or higher pressures may be used. Thus according to the process described in connection with Fig. l, the pressure in the portions 1I of the apparatus following the purifier tower'D may be gradually diminished until it is substantially atmospheric in condenser H.

The invention has the advantage that it provides a commercially practical and economical process and apparatus for the production of concentrated and relatively dilute hydroiluoric acid. Insofar as is known, highly concentrated hydroiiuoric acid has not heretofore been produced commercially by a continuous process such as herein described. The use of super-atmospheric pressure in the reaction zone, as described in connection with Fig. 1, leads to the production of amore highly concentrated hydrofluoric acid directly and thereby increases the efilciency of operation.

By the terms continuous and continuously, as used throughout the speciication and claims with reference to the introduction of the reactants into the reaction zone and the withdrawal of the reaction products, it is intended to include the addition or withdrawal of these materials at intervals, as in a semi-continuous process, as well as their-uninterrupted introduction and/or withdrawal.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as described in the following claims.

I claim:

1. In a process for'producing concentrated hydrouoric acid, the steps which comprise reacting together concentrated sulfuric acid and a mineral fluoride under continuously maintained super-atmospheric pressure, subjecting the evolved vapors to -a preliminary cooling at a temperature not below he boiling point of hydrofluoric acid or more than about 15 above the boiling point of hydrofluoric acid under the pressure conditions used, removing the condensate, further cooling'the residual vapors to a temperature below about 20 C., and recovering the resultant product.

2. In a process for the production of hydrofluoric acid having a concentration higher than the steps which comprise subjecting a substantially silica free fluorspar comprising substantially calcium iluoride to treatment with sulfuric acid under continuously maintained superatmospheric pressure at a temperature above about C., the amount of water present being such that the evolved gases contain less than about 15% Water, subjecting the evolved vapors to a preliminary cooling at a temperature above but not more than about 15 higher than the boiling point of hydroiiuoric acid under the pressure conditions used, removing the condensate. and condensing the residual vapors at a temperature below about 20 C.

3. A continuous process for producing concentrated hydrofloric acid, which comprises continuously reacting concentrated sulfuric acid and a ilnely divided substantially silica-free mineral fluoride under continuously maintained super-atmospheric pressure, continuously withdrawing the evolved vapors from the reaction zone, continuously removing sulfuric acid from the evolved vapors without substantial condensation of the remaining gases, cooling the remaining gases to a temperature above but not more than about 15 higher than the boiling point of hydrofluoric acid, continuously removing the condensate, and further cooling .the residual vapors toa temperature below about 20 C.

'4. A continuous process for producing anhydrous hydrouoric acid which comprises continuously introducing sulfuric acid having a concentration of about 98% and about equi-molecular proportions of a finely divided mineral fluoride comprising substantially calcium iluoride into one end of a longitudinal reaction zone, continuously withdrawing the evolved vapors near the zone of introduction of the reactants, continuously forcing the reaction mixture through the longitudinal zone of reaction away from the zone of introduction of the reactants, continuously withdrawing the solid residue comprising substantially calcium sulfate from the other end of the longitudinal reaction zone, while continuously maintaining super-atmospheric pressure in the reaction zone and a temperature in the reaction zone varyingy from about C. to about 160 C. at the zone of introduction of the reactants to about 310 C. to about 320 C. at the zone of eduction of the solid residue, continuously removing sulfuric acid from the evolved vapors without substantial condensation of the remaining gases, cooling the remaining gases to a temperature above but not more than about 15 higher than the boiling point of hydrofluorlc acid, continuously removing the condensate, further cooling the residual vapors to a temperature below about 20 C. but at a temperature sulciently high to preserve the condensate in liquid form, and recovering the condensate.

5. In a process of producing highly concentrated hydroiluoric acid from gases containing chiefly hydrogen iluoride together with some water vapor and small amounts of mineral acids obtainable by the reaction of concentrated sulfuric acid and a mineral fluoride, the step which comprises subjecting said gases to a preliminary cooling at a temperature above but not more than about 15 higher than the boiling point of hydrorluoric acid under the pressure conditions used, removing the condensate, and condensing the residual gases at a temperature belowabout 20 C.

6. In a process of producing highly concentrated hydrofluoric acid, the step which comprises subjecting gases containing chieily hydrogen iluoride together with not more than about 5% water vapor, obtainable by the reaction of concentrated sulfuric acid with a mineral fluoride, to a preliminary cooling at a temperature above but not more than about 15 higher than the boiling point of hydroiluoric acid under the pressure conditions used, removing the condensate, and condensing the residualgases at a temperature below about 20 C.

7. In a process of producing highly concentrated hydroiluoric acid, the step which comprises subjecting gases containing chieily hydrogen 'iluoride together with less than 15% water vapor and small amounts of mineral acids, obtainable by the reaction of concentrated sulfuric acid with substantially silica-free calcium fluoride to a preliminary cooling at a temperature between about 25 C. and 35 C., removing the condensate, and condensing the residual gases at a temperature below about 20 C. f

8. In a process of producing substantially pure. water-free hydrofiuorlc acid, the step which comprises subjecting a gaseous mixture containing approximately 94% hydrofluoric acid, approximately 5% water and a small amount of sulfurie acid, to a preliminary cooling at a um. 75

perature between about 25 C. and about 35 C., removing the condensate, and. condensing the residual gases at a temperature below about 20 C. v

9. In. a process ofproducing highly concentrated hydrouoric acid by the reaction of an acid with a uoride followed by a preliminary cooling of the evolved vapors at a temperature above the boiling point of hydrofiuoric acid to remove water vapor, then final condensation of-the hydrogen uoride, the step which comprises continuously maintaining super-atmospheric pressure in the zone of reaction between the said acid and lthe said uoride.

10. In a process of producing highly concentrated hydrofluoric acid lby the reaction of concentrated sulfuric acid with a substantially silica-free fluoride followed by a preliminary cooling of the evolved vapors at a temperature above the boiling point of hydrofiuorlc acid to remove water vapor, then inal condensation of the hydrogen uoxide, the step which comprises continuously maintaining a super-atmospheric pressure in the zone of reaction between the said acid 10 and the said fluoride.

. J C. LAWRENCE. 

